On the circuit board and the LSI chip such as a ball grid array (BGA), a number of projections such as minute bumps are provided so as to be used as electrodes for wiring. To measure the height of the projection formed on the surface of a certain workpiece in this manner is important when confirming that the projection having dimensions meeting the specification is formed for each lot. Particularly, when there is a variation in the dimensions of a number of projections formed on the circuit board and the LSI chip as the electrodes for wiring, this might cause an unfavorable electric contact, so that it is necessary to measure the height of the individual projection at a stage of quality inspection before shipping.
Herein, as the conventional method for measuring the height of such a projection, by imaging an area on the surface of the workpiece including the projection, which is an object to be measured, and performing a binary step based on brightness values in the image as obtained, the area in the image is classified into a bright area and a dark area, and by regarding the area in the image composed of the dark area as a projection area corresponding to the projection, and regarding an area composed of the bright area as a work area corresponding to the workpiece, the projection area is extracted, and the height of the projection is calculated based on the projection area.    [Patent Document 1] Japanese Patent Provisional Publication No. 2005-61953